Reliability evaluations have been carried out for determining whether soldered components keep necessary properties and functions under certain conditions, and various tests are conducted depending on the intended application. For instance, the strength of a joint portion is examined. In a heat cycle test, for example, a low temperature state and a high temperature state are repeated at regular intervals, and the number of cycles required for a soldered joint portion to reach a predetermined state (predetermined strength) is taken as the criterion for strength. In general, the type of desired reliability differs depending on usage, and the optimal composition of solder alloy is determined in accordance therewith. Accordingly, a variety of compositions of solder alloys that can achieve the optimal reliability have been studied and proposed, one example of which is described in Patent Literature 1.
In the Patent Literature 1, claim 1 discloses “a high-temperature solder comprising an alloy having a composition containing more than 3.0 wt % but not more than 5.0 wt % of Ag and 0.5 to 3.0 wt % of Cu, with a balance of Sn, and being capable of forming a soldered portion excellent in thermal fatigue-resistance,” and claim 2 discloses “the high-temperature solder according to claim 1, further comprising 5% or less of Sb.”
The Patent Literature 2 discloses an LED component in which “an electrode structure of an insulated substrate constituting a front surface implementing type device, in which a semiconductor chip is implemented on the insulated substrate, is formed to have an electrode structure of high reliability, in which the front surface electrode and the back surface electrode thereof are connected with each other through a plurality of connection electrodes, and further, in such an electrode structure, inspection for a bad connection can be reliably performed between the front surface electrode or back surface electrode and any of the plurality of connection electrodes.”